The invention relates to a diagnostic x-ray installation comprising a television pickup installation, image storage means, a difference stage for the subtraction of two chronologically successively obtained image signals through difference formation, and a monitor. Subtraction images are required, in particular, in the case of angiography in order to make blood vessels clearly visible which can only be poorly recognized in the normal radiograph, or on which bone structures are superimposed.
In the production of subtraction images, radiographs, which are prepared with contrast medium filling of the respective body region, are stored and subtracted from images which are taken without contrast medium filling. A subtraction of two picture records can proceed by photographic or television-technical means. In the case of the television-technical subtraction predominantly employed today, as storages for the images, either photographic documents which are scanned by television cameras or video image storages are employed.
In the brochure "Subtraskop", Order No. MR 57/1281 of Siemens AG, an x-ray diagnostic installation of the type initially cited is described wherein, serving as image storage means, are two photographic records which are synchronously taken by the television pickup installation; namely, by two television cameras. The image point data of both records are converted into corresponding electric pulses and subtracted from one another in an electronic differential amplifier. The difference image is represented on a monitor and predominantly contains only the representation of the body region filled with contrast medium; in particular, the blood vessels.
In order that similar structures of the television pictures can be cancelled, the pictures must be subtracted in coincidence. The coincident adjustment, in the case of the known apparatus, proceeds by manual adjustment means which effect a displacement of the pictures relative to one another. By means of these adjustment means, the operator must correct the image registration through adjustment of the subtraction images and visual comparison on the monitor. This signifies an undesired additional outlay.